linux-kernel - Re: [PATCH v2 1/1] KVM: x86/xen: add support for 32-bit guests in SCHEDOP

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Date:   Fri, 25 Nov 2022 12:34:21 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     "Kaya, Metin" <metikaya@...zon.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Cc:     "Durrant, Paul" <pdurrant@...zon.co.uk>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v2 1/1] KVM: x86/xen: add support for 32-bit guests in
 SCHEDOP_poll

On Thu, 2022-11-24 at 00:33 +0000, David Woodhouse wrote:
> Could do with a test case. It's fairly simple to flip the 'longmode'
> config even when the guest is actually in 64-bit mode, so it should be
> fairly easy to add this in the xen_shinfo_test.

Hm, not so. This doesn't depend on the 'longmode' flag; that's only for
the structs in shared memory. For an actual hypercall, the compat
behaviour depends more sensibly on the actual CPU mode in which the
hypercall was made.

I'm not sure I see how to use 32-bit guest mode from the KVM self
tests. Even KVM_HC_SEND_IPI doesn't seem to have a 32-bit test... or a
positive test at all, in fact. All we seem to do is test that it
returns -ENOSYS when *disabled*.

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